The problem of proliferative diabetic retinopathy is addressed in experimental studies utilizing several types of neovascularization. Special attention will be given to the model of retinal neovascularization in the young beagle. Major emphasis is directed toward the development of effective inhibitors of this retinal neovascularization that develops following oxygen exposure to young, pure strain beagles. The beagle model will be used primarily because the retinal neovascularization at the disc and elsewhere in the retina of classical human diabetic retinopathy. The proliferative lesions can be precisely localized at the disc or elsewhere in the fundus and develop in 100% of the animals exposed. Preliminary studies suggest that adult rabbit vitreous contains an inhibitor of neovascularization. Further documentation of this inhibition will be done and extended to a comparison with other species. Other possible inhibitors of neovascularization, e.g., cartilage extract, will be tested in the above beagle model of retinal neovascularization after preliminary testing in the more economical and simpler assays, such as tissue culture and the corneal preparations to identify the most suitable materials to develop for future evaluation in selected patients with proliferative diabetic retinopathy.